on line Chapter 3 integumentary system 2010-6-20修改.doc

Chapter 3 Integumentary SystemAnatomy and Physiology of the Integumentary SystemInzootomy, the integumentary system is the external covering of the body, the name derives from theLatinintegumentum, which means a covering. This most extensive organ system has the skin and accessory structures, including hair, nails, sweat glands and sebaceous glands. In fact the skin is the largest organ in the body: 12-15% of body weight, with a surface area of 1-2 meters. The integumentary system has multiple roles in homeostasis, including protection, sensory reception, temperature regulation and fluids secretion. The primary function is protection of internal structures, prevention of entry of disease-causing microorganisms, it forms a two-way barrier that is capable of keeping pathogens and harmful chemicals from entering the body. It also stops critical body fluids from escaping the body and prevents injury to the internal organs lying underneath the skin. The sensory receptors that detect temperature, pain touch and pressure are located in the skin. The messages for these sensations are conveyed to the spinal cord and brain from the nerve endings in the middle layer of the skin. The structure of the skin also aids in the regulation of the body temperature through a varieties of means. The evaporation of sweat cools the body. The body also lowers its internal temperature by dilating superficial blood vessels in the skin. This brings more blood to the surface of the skin, which allows the release of heat. If the body needs to conserve heat, it constricts superficial blood vessels in the skin, keeping warm blood away from the surface of the body. Finally, the continuous fat layer of the subcutaneous layer of the skin acts as insulation. Fluids are produced in two types of skin glands: sweat and sebaceous. Sweat glands assists the body in maintaining its internal temperature by creating a cooling effect when sweat evaporates, it also acts as a mini-excretory system; urea, salts, and water are lost through the skin pores in sweat. The sebaceous glands, or oil glands, produce a substance called sebum. This oily substance lubricates the skin surface. The skin has other functions as well. For example, the skin also has important metabolic duties. Like liver cells, it carries out some chemical conservations that activate or inactivate certain drugs and hormones, and it is the site of vitamin D synthesis in the body. The Anatomy of Skin Skin is continuous with, but structurally distinct from mucous membranes that line the mouth, anus, urethra, and vagina. Moving from the outer surface of the skin inward, the three layers are as follows(see figure 3.1): 1. Epidermis: the thin, outer membrane layer 2. Dermis or corium: the middle, fibrous connective tissue layer.3. Subcutaneous layer: the innermost layer, containing fatty tissue. Figure 3.1 Skin Structure. Three-dimensional view of the skin and the underlying subcutaneous layer ( or hypodermis). Epidermis The epidermis is the outermost, totally cellular layer of the skin, it doesnt have a blood supply or any connective tissue, so it is dependent for nourishment on the deeper layer of the skin. The epidermis is composed of 4 to 5 layers (strata) of squamous epithelial cells, these flat scale-like cells are arranged in overlapping layers or strata. The deepest layer in the epidermis, the stratum basale, or basal layer, produces new cells. As these cells gradually rise toward the surface, they die and become filled with keratin, a protein that thickens and toughens the skin and make the skin waterproof. The outermost (horny) layer of the epidermis, the stratum corneum, is composed of flat, dead, protective cells that are constantly being shed and replaced. The basal layer also contains special cells called melanocytes, which produce melanin, the black pigment that gives color to the skin and protects against damage from the ultraviolet rays of the sun. DermisThe dermis, also referred to as the corium, is located between the epidermis and subcutaneous layer. Its name means “true skin”. Unlike the thinner epidermis, the dermis is living tissue with good blood supply. This layer supplies support and nourishment for the skin. The dermis itself is composed of connective tissue and collagen fibers. Collagen fibers are made from a strong fibrous protein present in connective tissue, forming a flexible “glue” that gives connective tissue its strength. The dermis houses hair follicles, sweat glands, sebaceous glands, blood vessels, lymph vessels, sensory receptors, nerve fibers, and muscle fibers. Subcutaneous LayerThe subcutaneous layer (hypodermis) lies beneath the dermis. Loose connective tissue such as adipose tissue (fat) insulates the body, conserving heat. It also contains blood vessels, lymph vessels, and the bases of hair follicles and sweat glands. The fat distribution in this layer gives the female form its characteristic curves.Accessory structuresThe accessory structures of the skin are the anatomical structures located within the dermis. This includes hair, nails, sweat glands and sebaceous glands. Hair is widely distributed over the body. Each hair develops within a sheath or hair follicle and grows from its base within the deep layers of the skin. Both hair and nails function in protection. Each nail develops from a growing region at its proximal end. Hair and nails are composed of nonliving material consisting mainly of keratin. The sweat glands act mainly in temperature regulation by releasing a watery fluid that evaporates to cool the body. The sebaceous glands release an oily fluid, sebum, that lubricates the hair and skin and prevents drying. KeyHair Hair sheds and is replaced constantly during growth and rest phases. Hair has a protective function: eyebrows keep sweat from running into the eyes, nose and ear hairs filter dust from the air, and scalp hairs protect against abrasion and overexposure to sun rays. Hair is mainly composed of the protein keratin. Hair growth begins under the skin at the root. Each individual strand of hair is housed in a hair follicle. Only the “living” portion of the hair is found in the follicle. The hair that is visible is the hair shaft, as it exhibits no biochemical activity, it is considered dead. The base of the root is called the bulb, which contains the cells that produce the hair shaft. Other structures of the hair follicle include the oil producing sebaceous gland which lubricates the hair and the arrector pili muscles, which are smooth muscle cells attached to hair follicles. When they contract, they pull the hair into an upright position, causing skin dimples (goose bumps). The nervous system regulates these muscles; cold temperatures or fright can activate them. Each strand of hair is made up of the medulla, cortex, and cuticle. The medulla is the innermost region of the hair strand. Many hair fibers have little or no medulla. The cortex, or middle layer of the hair, is the primary source of mechanical strength, water uptake and hair color. The cortex contains melanin, which colors the fiber based on the number, distribution and types of melanin granules. The hair root in a hair follicle is embedded beneath the skin, hair follicles extend into the dermis; the deep ends expanded parts are called hair bulbs. At the base of the follicle is a projection (formed like sticking a finger in the bottom of a stocking and pushing it in a small amount), which is called a papilla and it contains capillaries, or tiny blood vessels, that feed the cells. The living part of the hair is bottom part surrounding the papilla called the bulb. This bottom part is the only part fed by the capillaries. The cells in the bulb divide every 23 to 72 hours, faster than any other cells in the body. In other words, a papilla (connective tissue protrusion that contains capillaries) protrudes into the hair bulb and provides nutrients for the growing hair. The deeper cells in the hair root force older keratinized cells to move upward, forming the hair shaft.NailLike hair, nails develop from the epidermis. These hard plates of keratinized cells are at the ends of fingers and toes. Nails appear pink because their translucency reveals the vascular tissue beneath. They aid in grasping objects, scratching, and protecting fingers and toes.The components of the nail are the lunula, body, root, and free edge. The lunula is the white half-moon shaped part at the nail base. Both the body and free edge region that overhangs the end of the finger or toe are visible. The nail rests on the thick layer of epithelial skin called the nail bed. The root is hidden under skin folds. Eponychium (thin layer of epithelium) covers the nail during development; in the adult, it remains at the nail base only and is called the cuticle. The hyponychium is the epithelium of the nail bed.Sebaceous GlandsSebaceous glands, found in the dermis, secrete the oil sebum. These oil ducts open into hair follicles and lubricate the hair and skin, thereby helping to prevent drying of the skin. Secretion from the sebaceous glands increases during adolescence and begins to diminish as age increases. A loss of sebum in old age, along with sun exposure, can account for wrinkles and dry skin. Sweat glands About two million sweat glands are found throughout the body. The highly coiled gland is located in the dermis. Sweat travels to the surface of the skin in a sweat duct. The surface opening of a sweat duct is called a sweat pore. Sweat glands function in cooling the body as sweat evaporates. Sweat or perspiration contains a small amount of waste products but is normally colorless and odorless. Combining Forms Commonly Used in This SystemCombining form Meaning Example adip/o fat adiposealbin/o white albinism caus/o burn, burning causalgiacutane/o skin subcutaneousderm/o skin epidermisdermat/o skin dermatitisdisphor/o profuse sweating diaphoresis hidr/o sweat anhidrosisichthy/o scaly, dry ichthyosiskerat/o hard, horny tissue keratosisleuk/o white leukoplakia lip/o fat lipoma melan/o black melanocytemyc/o fungus dermatomycosisonych/o nail onycholysispil/o hair pilosebaceousrhytid/o wrinkle rhytidoplasty seb/o oil seborrheatrich/o hair trichomycosis xanth/o yellow xanthoma Suffixes Commonly Used in This SystemSuffix Meaning Example-derma skin scleroderma-opsy view of biopsy-plakia a plate leukoplakia-tome instrument used to cut dermatomeDiagnostic Procedures Relating to This SystemFungal scrapings Scrapings, taken with a curette or scraper, of tissue from lesion are placed on a growth medium and examined under a microscope to identify fungal growth. Needle biopsy Using a sterile needle to remove tissue for examination under microscope. Skin tests (ST) Test to determine the patients reaction to a suspected allergen by injecting a small amount under the skin (intradermal) with a needle. The reaction of the patient to this material is then read to indicate any allergy. Examples of such tests are the tuberculin (TB) test, Mantoux (PPD) test, patch test and Schick test.Sweat test Test performed on sweat to determine the level of chloride. An increase in skin chloride is seen with the disease cystic fibrosis. Pathology Relating to This System 1. Burn A burn is a type of injury that may be caused by heat, cold, electricity, chemicals, light, radiation, or friction. Burns can be highly variable in terms of the tissue affected, the severity, and resultant complications. Muscle, bone, blood vessel, and epidermal tissue can all be damaged with subsequent pain due to profound injury to nerve endings. Depending on the location affected and the degree of severity, a burn victim may experience a wide number of potentially fatal complications including shock, infection, electrolyte imbalance and respiratory distress. Beyond physical complications, burns can also result in severe psychological and emotional distress due to scarring and deformity.Burn, 1st degree damage to the epidermis layer of the skin. Characterized by hyperemia, but no blisters or scars. Burn 2nd degree damage extends through the epidermis and into the dermis, causing vesicles to form. Scarring may occur. Also called partial thickness burn. Burn 3rd degree damage to full thickness of skin and into underlying tissues. Infection is a major concern with 3rd degree burns, and fluid loss can be life threatening. Grafts are usually required and scarring will occur. Also called full-thickness burn. Treatment of Burn A local anesthetic is usually sufficient in managing pain of minor first-degree and second-degree burns; also Aloe vera sap can be used to heal the burn area. However, systemic anti-inflammatory drugs such as naproxen may be effective in mitigating pain and swelling. Additionally, topical antibiotics such as Mycitracin are useful in preventing infection to the damaged area. Lidocaine can be administered to the spot of injury and will generally negate most of the pain. Regardless of the cause, the first step in managing a person with a burn is to stop the burning process at the source. For instance, with dry powder burns, the powder should be brushed off first. With other burns, such as those caused by exposure to chemicals, the affected area should be rinsed thoroughly with a large amount of clean water to remove the caustic agent and any foreign bodies. Cold water should not be applied to a person with extensive burns, however, as it may compromise the burn victims temperature status.If the patient was involved in a fire accident, then it must be assumed that he or she has sustained inhalation injury until proven otherwise, and treatment should be managed accordingly. At this stage of management, it is also critical to assess the airway status. Any hint of burn injury to the lungs (e.g. through smoke inhalation) is considered a medical emergency.To help ease the suffering of a burn victim, they may be placed in a special burn recovery bed which evenly distributes body weight and helps to prevent painful pressure points and bed sores. Survival and outcome of severe burn injuries is remarkably improved if the patient is treated in a specialized burn center/unit rather than a hospital. Serious burns, especially if they cover large areas of the body, can result in death.Once the burning process has been stopped, the patient should be volume resuscitated according to the Parkland formula, since such injuries can disturb a persons osmotic balance. This formula dictates the amount of Lactated Ringers solution to deliver in the first twenty four hours after time of injury. This formula excludes first and most second degree burns. Half of the fluid should be given in the first eight hours post injury and the rest in the subsequent sixteen hours. The formula is a guide only and infusions must be tailored to the urine output and central venous pressure. Inadequate fluid resuscitation causes renal failure and death.2. AcneAlternative Names：Acne vulgaris; Cystic acne; Pimples; ZitsCauses Acne occurs when tiny holes on the surface of the skin called pores become clogged. Each pore is an opening to a canal called a follicle, which contains a hair and an oil gland. Normally, the oil glands help keep the skin lubricated and help remove old skin cells. When glands produce too much oil, the pores can become blocked, accumulating dirt, debris, and bacteria. The blockage is called a plug or comedo.The top of the plug may be white (whitehead) or dark (blackhead). If it ruptures, the material inside, including oil and bacteria, can spread to the surrounding area and cause an inflammatory reaction. If the inflammation is deep in your skin, the pimples may enlarge to form firm, painful cysts.Acne commonly appears on the face and shoulders, but may also occur on the trunk, arms, legs, and buttocks. Acne is most common in teenagers, but it can happen at any age, even as an infant. Three out of four teenagers have acne to some extent, probably caused by hormonal changes that stimulate oil production. However, peoplein their30s and 40s may also have acne.Acne tends to run in families and can be triggered by:Hormonal changes related to menstrual periods, pregnancy, birth control pills, or stress Greasy or oily cosmetic and hair products Certain drugs (such as steroids, testosterone, estrogen, and phenytoin) High levels of humidity and sweating Despite the popular belief that chocolate, nuts, and other foods cause acne, this does not seem to be true.Symp